1. Field of the Invention
This invention relates to implantable medical devices such as stents. More particularly, the invention relates to materials that can be used to coat stents.
2. Description of Related Art
In the field of medical technology, there is frequently a necessity to administer drugs locally. To provide an efficacious concentration to the treatment site, systemic administration of medication often produces adverse or toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. For the treatment of vascular lesions, stents can be modified with a polymeric coating to provide local drug delivery capabilities.
Examples of polymers that can be used to coat stents or other implantable devices include hydrophobic polymers, for example, poly(meth)acrylates, such as poly(n-butyl methacrylate) (PBMA) and copolymers or terpolymers having units derived from n-butyl methacrylate (BMA). PBMA and BMA-based coatings can provide effective control of the rate of release of a drug from a stent. In addition, PBMA and BMA-based polymers are biocompatible, have good adhesion to the underlying stent surface, are easily processable, and possess good physical and mechanical properties such as ability to withstand elongation, compression, and shear that the stent undergoes during crimping onto the catheter, delivery to the lesion site, and expansion.
The properties of PBMA and BMA-based stent coatings can be improved, however. For example, permeability of such coatings can be too low, particularly for drugs having higher molecular weights, leading to potentially insufficient supply of the drug to the diseased site. An ability to better regulate the rate of release through the coatings is desired. The present invention provides such coatings.